More and more electronic applications are requiring distributed power architectures where the current requirements of the electrical loads are requiring the power supplies to be moved as close to the load as practicable. Instead of the single power supply which would accept ac line voltage and produce a dc or ac output voltage for use by an entire electrical system, today's ultra fast electronics and electrical components require their own power supply to accommodate the high transients in their load currents. This new concept in power systems is often referred to as a "distributed power architecture." This type of power architecture can be implemented by means of a system rectifier that converts the ac line current into an unregulated or slightly regulated dc voltage, and numerous "point-of-load" power supplies. The point-of-load power supplies accept the dc voltage from the rectifier and produce a highly regulated dc voltage which is able to accommodate very large current transients (large di/dt).
The point-of-load power supplies need to be small, have a high power density, and be mountable on the circuit boards near the load. In addition, the point-of-load power supplies should be modular to allow two or more to be connected in parallel to supply power to high current loads, or to provide redundancy. This modularity allows a single design to be adapted for loads with varying current requirements. These small modular power supplies, however, present numerous design issues. Their high power density and small size, force pin footprints to be minimized, and when placed in parallel they must be forced to share current effectively.
The small size and high power density requirement forces the power modules to sacrifice features both due to lack of space on the circuit board as well as to minimize the number of pins, as well the pin footprints, so that the modules take up as little space as possible on the system board to which they will be mounted. Further, small variances in component values or reference levels will cause one or two paralleled power supples to supply the majority of load current while some of the remaining modules supply relatively little, or no, current. This disparity in load currents causes the modules supplying the majority of the current to wear faster due to the increased thermal stresses, leading to premature failures in the field.
Accordingly, what is needed is a power supply module that minimizes the pin footprint and shares current effectively when placed in parallel with other power supply modules.